1. Field of the Invention
The present invention relates to the control of fuel burning devices in general and in particular relates to a fuel oil burner using a hot surface ignitor electrode that is sintered to full density with no porosity and which further includes a control assembly that preheats the ignitor and then provides a trial ignition during which time the blower motor and the fuel oil are provided to the combustion chamber. If a flame is not detected in less than one second, the device is de-energized and starting must be retried.
2. Description of Related Art
Portable forced air kerosene heaters typically comprise an outer housing surrounding a combustion chamber. Air is forced into the combustion chamber. A burner is located at one end of the combustion chamber and the burner normally has a fuel nozzle frequently incorporating eductor means providing jets of air to draw, mix, and atomize the fuel delivered by the nozzle. The nozzle, together with the eductors, discharges a combustible fuel-air mixture into the combustion chamber. An ignitor is provided to ignite the mixture and, after initial ignition, continuous burning occurs. Typically, during the continuous combustion, forced air heat currents issue from the end of the heater opposite the burner and additional heat radiates from the surface of the heater housing.
Portable space heaters of the general type described are frequently provided with a direct spark type of ignitor and a motor. The motor normally runs a fan supplying air to the combustion chamber and the eductors and operates a fuel pump or air compressor to supply the fuel to the combustion chamber.
When the portable space heater is functioning properly, fuel burning will occur near the end of the combustion chamber at which the burner is located. In the event of reduced air flow, however, the flame will move toward the opposite end of the combustion chamber, the oxygen supply becoming inadequate for proper combustion. Under such a circumstance, it is desirable to shut down the heater. Inadequate air may result because of a malfunction of the fan or a blocking of the passages for air into or out of the combustion chamber.
Inadequate operation and possibly dangerous conditions may also be indicated by a lower than normal temperature of the burner flame, representing improper combustion conditions.
It is also desirable to shut down the portable space heater when there is a flame failure. This can occur by virtue of faulty ignition, a blockage of the fuel nozzle, or exhaustion of the fuel supply.
Further, many of the prior art portable, fuel oil fired, heaters utilize a spark gap for ignition. (Some use heating coils that glow at a particular temperature sufficiently hot to cause ignition of gaseous-type fuel.)
Hot surface ignition systems (HSI) have been used for more than twenty years for gas ignition in units such as gas clothes dryers, gas ovens, gas fired furnaces, and boilers thus replacing and eliminating standing gas pilot lights. Low voltage ignitors (12 and 24 volts) of the hot surface type are made from a patented ceramic/intermetallic material. These ignitors were used in compact low wattage assemblies for gas fired ignition. The element reaches ignition temperature in less than 3-5 seconds and utilizes about 40 watts of power. The ignitor is made from a composite of strong oxidation resistant ceramic and a refractory intermetallic. Thus hot surface ignitors have no flame or spark. They simply heat to the required temperature for igniting a fuel air mixture. Such ignitors have not been used in oil burning systems because the ignitor material is porous and oil entering the porous cavities causes buildup of the materials that are inimical to the operation of the burner.
A 100 to 240 V HSI ignitor has been developed in which the material is compressed and sintered to full density leaving no porosity resulting in a high performance ceramic composite. It can operate at very high temperatures such as 1,300.degree. to 1,600.degree. C. The application of such high voltage hot surface ignition device is especially attractive for use in the present invention wherein oil fuel burning heaters are to be constructed. They provide unique advantages over prior art gas flames, heating coils, and spark gap ignition systems.
In any case, malfunctions in the prior art heaters can cause insufficient or incomplete burning or a failure to burn issuing fuel thus producing a dangerous existence of highly flammable liquid or noxious fumes. Prior art devices include a number of safety control circuits for fuel burning devices proposed to avoid the many and often undesirable results of improper burning or failure of flame in apparatus such as portable space heaters.
Thus, in U.S. Pat. No. 3,713,766 a pretrial ignition period is determined by a bimetallic thermal switch which, after a predetermined period of time if ignition has not started, opens and removes the power. Manual resetting of the bimetallic contacts is required to restart. However, during burner operation, if the flame for any reason goes out, a new trial period is automatically reinitiated. This could be dangerous if a fuel buildup in the combustion chamber is ignited. Further, if the photocell detecting the flame is shorted during operation, the burner will continue to operate because the circuit cannot detect that the photocell has been shorted. In such case, the unit thinks that there is a flame because, when there is a flame, the photocell resistance is very low, similar to a short. This control requires a dark chamber to start. However, this control does not lockout if start-up is negated because of light in the chamber, undesirable results can occur. Thus in a case where a cover was removed, the control can start the motor if a person comes close enough to block the light. Further, spark ignition is constantly applied during each cycle of the line voltage applied. Finally, there is an electric spark ignition circuit.
In U.S. Pat. No. 3,651,327, a fluctuating control signal, due to flame fluctuation, is rectified and energizes a control device that is a relay. This circuit is entirely a DC circuit. It responds only to the presence or absence of a flame and would require a separate circuit for a trial ignition period. It has no start-up circuit or restart circuit, no preheat circuit and no hot surface ignition.
In U.S. Pat. No. 3,672,811, apparently a gas-type heater, if the photocell shorts during operation, there is no detection of loss of flame. Thus there is no shutdown of the fuel flow or the air blower. It also uses spark gap ignition with a continuous spark being applied. There is no hot surface ignition.
In U.S. Pat. No. 3,741,709 there is no shutdown of the control system if the photocell shorts during operation. There is no ignition preheat period, no ignition trial period, constant ignition, and no hot surface ignition device.
In U.S. Pat. No. 3,393,039, if the unit fails to start during an ignition period, a resistance heater opens the contacts of a thermal contact unit to remove power. It utilizes only AC voltage, uses a mechanical relay to cause continued operation of the circuit by detecting the heat of the flames and has an automatic restart. It is not shutdown during operation if the flame is gone. It simply keeps trying to ignite. There is no hot surface ignition.
In U.S. Pat. No. 3,537,804, an ignitor coil is used rather than a spark gap or pilot flame. The temperature of the ignitor coil is sensed by a photocell and, when the proper temperature is reached, the fuel valve is opened. It has a trial ignition in which, if a flame does not occur, a heating element opens bimetallic contacts to remove power. If the photocell is shorted during operation, the system simply tries to restart and does not shut down unless the bimetallic switch is opened after a heating element in the circuit reaches a predetermined temperature.